Transmitters are widely used in several application areas, like mobile radio or satellite technology. It is important for systems of such technology areas that energy consumption is small due to the limited power supply. Thus, it is an ongoing concern of the industry to reduce power consumption of transmitters.
One possible solution is to use power efficient amplifiers, like switching power amplifiers. However, switching power amplifiers has to be driven by a signal comprising a good linearity. Due to this fact suitable modulation methods, like pulse width modulation (PWM) or pulse density modulation (PDM) are essential.
Moreover, it is an ongoing concern of the industry to increase the transfer rate. One possibility is to use the amplitude and the phase as well as information carriers to achieve a more efficient modulation scheme. However, this implicates linearity issues, in particular in connection with switching power amplifiers.
In prior art several solutions are used, like combined analogue loop universal modulator (CALLUM) or sigma delta. The needed linearity of the signals being transmitted is obtained by implementing a feedback loop. However, the used feedback loops encompass issues of loop stability and operate over a large range.
Document WO 20051119904 discloses a PWM modulator with power combining at the output of two power amplifiers. A feedback loop is arranged to obtain the needed linearity of the depicted radio frequency (RF) input signal. However, implementing the shown architecture is complex. According to the shown PWM modulator, a feedback loop is essential to obtain the needed linearity.
It is one object of the present application to provide reduced power consumption of the apparatus. A further object is to increase the linearity of the signal being amplified. A further object is to increase the dynamic range of the apparatus.